A note on the effect of plane of nutrition on fractional outflow rates from the rumen and urinary allantoin excretion by wether sheep

During a series of routine experiments to evaluate 16 foods offered to wether sheep, conventional measurements of digestibility were augmented by measurement of fractional outflow rates (FOR) of solids (ks) and liquid (k1) from the rumen and urinary allantoin nitrogen excretion (UAN) as an index of microbial yield. Fixed (1 kg) amounts of ‘dry’ foods were offered to sheep ranging in weight from 42 to 89 kg which permitted a retrospective analysis of plane of nutrition effects on diet digestibility, ks, k1 and UAN. Each diet was simultaneously offered to three sheep (one each of large, medium and small size). Smaller sheep had significantly higher FOR, significantly lower apparent digestibilities of dry matter and significantly higher UAN (g/kg digestible organic matter (DOM)). Higher UAN (g/kg DOM) indicated higher microbial energetic efficiencies with the smaller sheep.